My notes when reading from “Michael Doyle” book –
Thanks Michael for writing such a nice book.
Below are some points which I want to remember always J . Plan is to write
such point from each chapter. I hope it will help others.
Recovery time Objective - > uptime of server.
·
99.9% -> 8.76 hours in year
·
99.99% -> 53 minute in year
·
99.999%-> 6minute in year
Recovery Point Object- > calculation of RPO depends on-
·
Amount of data lost
·
Cost to the company of lost data
·
Cost to the company for the time to recover
data.
SQL server mirror
- > As per
TechNet this feature is going to be removed from future version , plan to use
“AlwaysOn Availability group “.Mirroring is implemented on a per-database basis and works only with
databases that use the full recovery model.
Database
mirroring maintains two copies of a single database that must reside on
different server instances of SQL Server Database Engine. Typically, these
server instances reside on computers in different locations. Starting database
mirroring on a database, initiates a relationship, known as a database mirroring session, between these server
instances. Database mirroring involves redoing
every insert, update, and delete operation that occurs on the principal
database onto the mirror database as quickly as possible. Redoing is
accomplished by sending a stream of active transaction log records to the
mirror server, which applies log records to the mirror database, in sequence,
as quickly as possible. Unlike replication, which works at the logical level,
database mirroring works at the level of the physical log record. Beginning in
SQL Server 2008, the principal server compresses the stream of transaction log
records before sending it to the mirror server.
Sql Server Clustering : two or more SQl Server node that act as a
single Sql server instance. A Sql server cluster contains –
·
A
network name for cluster instance.
·
One
or more IP address for cluster instance.
·
A
combination of one or more disk.
·
At
least one sql server with one SQL server Agent, Full text search service.
·
Registry
key for checkpoints across nodes and dlls for failover process.
AlwaysOn [SQL server 2012]: Database mirroring +
A database can
use either “AlwaysOn” or Database mirroring, not both.
SQL server log Shipping : SQL Server Log shipping allows you to
automatically send transaction log backups from a primary
database on a primary server instance to
one or more secondary databases on separate secondary server instances. Log Shipping can be combined with DB mirroring.
Log Shipping
versus Database Mirroring –
1.
Infinite
number of receivers in case of log shipping.
2.
Failover
is always manual.
3.
Failover
duration is slow as compared to database mirroring.
4.
Log
shipping use both committed and uncommitted transactions, db mirroring just use
committed transactions.
SAN [Storage Area
Network]: set of disk and tape can be viewed as single entity. Accessed at file
block level.
RAID Redundant
Array of inexpensive Disk
RAID 0 : disk
stripping as writes blocks of data across disks.
RAID 1: Disk
Mirroring, requires two disk, every bit is written over two disks.
RAID 5: data
stripping with parity. Data is written over 3 disks.
RAID 10:
equivalent to RAID 0 +1. Two sets of disk each with RAID 0 configuration.
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